Polyolefin-based resins find uses in a wide variety of applications because of their characteristics such as satisfactory processability, satisfactory physical properties, and low specific gravity. Polyolefin-based resins also include various resin species such as polyethylene and polypropylene so that it is possible to select physical properties suitable to each application. Polyolefin-based resins are, however, easily flammable materials, and therefore, imparting flame retardancy has been contemplated so far in various ways.
As an example for imparting flame retardancy, addition of a halogen-based flame retardant has been conventionally contemplated, but, in recent years, non-halogen-based flame retardants have been actively contemplated due to environmental problems such as emission of toxic gases on combustion. As an exemplary non-halogen-based technique for imparting flame retardancy for polyolefin-based resins, most frequently conducted is a method of adding a metal hydroxide such as magnesium hydroxide and aluminum hydroxide. Although many reports have been made on this approach for imparting flame retardancy in particular as a technique for wire-coating materials, these flame-retardant resin compositions containing magnesium hydroxide, aluminum hydroxide or the like require addition of a large amount of a flame-retardant to achieve flame-retardant performance. This has led to reduction in the physical properties of the resin composition, resulting in a problem in which characteristics inherent to the resin are not achieved, a problem in which processability, which is a feature of polyolefin-based resins, is impaired, and the like. Accordingly, although it is possible to extend application of a polyolefin-based resin composition containing a metal hydroxide into wire coating materials, it has been extremely difficult to extend the application into molded articles, fiber products and the like.
To solve such problems, a technique of imparting flame retardancy to a polyolefin-based resin by using a phosphoric acid ester-based flame-retardant has been contemplated. Phosphoric acid ester monomers, typified by triphenyl phosphate, are highly volatile, and have caused problems such as mold deposit on molding and bleeding out during use of molded articles. Accordingly, condensed phosphoric acid ester-based flame retardants have been contemplated. Unfortunately, when a condensed phosphoric acid ester-based flame retardant was used, there were problems such as an insufficient flame-retardant effect and reduced heat resistance due to the plasticizing effect of the phosphoric acid ester.
Thus, in recent years, there has been suggested an intumescent flame retardant which forms a foamed layer on the surface of a molded article during combustion by using a specific phosphate-based flame-retardant to suppress diffusion of decomposition products and heat transfer and to exert flame retardancy (PTL 1). Although having excellent flame retardancy, the intumescent flame retardant has problems such as insufficient dispersion into resin due to its secondary agglomeration, aggravated hygroscopicity due to hydrolysis and the like. Coaddition of a compound having a specific molecular structure such as phosphoric acid ester, silicone oil, polycarbodiimide or the like has made an improvement, but satisfactory characteristics have not been achieved so far (PTLs 2 to 4).
Furthermore, the aforementioned technology for imparting flame retardancy is not generally applicable to a variety of polyolefin-based resins, but can be applied only to specific resin species among polyolefin-based resins. Of these, highly heat-resistant polyolefin-based resins, typified by polymethylpentene resins, have a high processing temperature, which could not be addressed by phosphoric acid ester-based flame retardants.